1. CNTs David Shaw EE

2. Proposed System: Overview First elevator: 20 ton capacity (13 ton payload) Constructed with existing or near-term technology

4. Space Elevators

6. Challenges Induced Currents: milliwatts and not a problem Induced oscillations: 7 hour natural frequency couples poorly with moon and sun, active damping with anchor Radiation: carbon fiber composites good for 1000(?) years in Earth orbit (LDEF) Atomic oxygen protecyion: <25 micron Nickel coating between 60 and 800 km Environmental Impact: Ionosphere discharging not an issue(?) Malfunctioning climbers: up to 3000 km reel in the cable, above 2600 km send up an empty climber to retrieve the first Lightning, wind, clouds: avoid through proper anchor location selection Meteors: ribbon design allows for 200 year probability- based life Health hazards: under investigation but initial tests indicate minimal problem Damaged or severed ribbons: collatoral damage is minimal due to mass and distribution

7. Anchor Anchor station is a mobile, ocean- going platform identical to ones used in oil drilling Anchor is located in eastern equatorial pacific, weather and mobility are primary factors

15. CNT Properties

16. H. W. Zhu, Science, 296 (02)

17. Synthesis

18. Processing Techniques

19. Discharges Cheap Yield ~30% Short (<50 microns) Random deposits

21. CVD Growth Mechanisms

22. MWNTs by CVD Methods

23. Single Walled NTs

24. Heterostructure Carbon nanotubes

25. Alignment Growth

26. Masking Techniques

27. Catalytic CVD Growth Hongjie Dai, Stanford

28. Catalytic Methods High potential for scale-up production Long lengths Multiwall CNTs Many defects in the materials

29. Laser Ablation High (~70%) yield single- wall CNTs High costs

30. Scanning electron microscopy images of raw (on the left) and purified (on the right) SWNTs

33. CNT for electronics Carrier transport is 1-D. All chemical bonds are satisfied  CNT Electronics not bound to use SiO 2 as an insulator. High mechanical and thermal stability and resistance to electromigration  Current densities up to 10 9 A/cm 2 can be sustained. Diameter controlled by chemistry, not fabrication. Both active devices and interconnects can be made from semiconducting and metallic nanotubes.

34. Early chemical sensors were of the CHEMFET type with SnO 2 and other oxide conducting channels Similar CNT-FETs have been tested in the literature, exposing to NH 3, NO 2, etc.; change in conductivity has been observed Limitations of CNT-FET -Single SWCNT is hard to transfer or grow in situ -Even a film of SWCNTs by controlled deposition in the channel is complex -3-terminal device is complex to fabricate -Commercial sensor market is very cost sensitive Courtesy of M. Meyyappan

35. A relative resistance or current is measured from each sensor Using pattern matching algorithms, the data is converted into a unique response pattern Operation: 1.The relative change of current or resistance is correlated to the concentration of analyte. 2.Array device “learns” the response pattern in the training mode. 3.Unknowns are then classified in the identification mode. By the courtesy of Dr. M. Meyyappan @ NASA Ames Research Center

36. 12 to 36 sensing elements are on a chip (1cm x 1cm) now with heaters and thermistors. Number of sensing elements can be increased on a chip. Number of chips can be increased on a 4” wafer. Wafer size can be increased to 6”, 8”, or 12”. SWCNT solution-casting by ink jetting or using microarrays Courtesy of M. Meyyappan

37. O=N=O. NO2 P-type e E0E0 EVEV EFEF ECEC SWCNT O=N=O CH 3 O=N=O CH 3 e e Intratube ModulationIntertube Modulation Nitrotoluene Courtesy of M. Meyyappan

38. Spacing vs. Diameters

39. Catalysts and SWNTs

40. Nanotubes of various diameters adsorbed to a surface

41. Surface Bonding Characteristics

42. The insertion of a pentagon into the wall structure initiates tapering in the nanotube wall.

43. Why do Carbon Nanotubes form? Carbon Graphite (Ambient conditions) sp 2 hybridization: planar Diamond (High temperature and pressure) sp 3 hybridization: cubic Nanotube/Fullerene (certain growth conditions) sp 2 + sp 3 character: cylindrical Finite size of graphene layer has dangling bonds. These dangling bonds correspond to high energy states. Eliminates dangling bonds Nanotube formation + Total Energy Increases Strain Energy decreases

44. CNT Properties (cont.)

45. Transport on a single CNT